The surface of the fumed silica has a large amount of hydroxyl groups which form hydrogen bonds between the aggregates, and when sufficiently dispersed in the coating, a network of silica is formed.
On the one hand, during the construction process, the solvent is easily moved to the edge due to the faster evaporation of the solvent at the edge of the coating. The silica network can effectively prevent the movement of the coating to form a side, and at the same time prevent the sag of the coating during the curing process and make the coating uniform.
On the other hand, fumed silica increases the medium-low shear viscosity of the system due to the formation of hydrogen bonds, which acts as a thickening effect and produces a thixotropic phenomenon. Therefore, fumed silica is widely used in oily systems.
In addition, fumed silica has a large specific surface area, high surface energy, and is very easy to agglomerate, and must be properly dispersed during application to achieve the best results. In the paint production process, the surface treatment of the fumed silica, the addition method, the selection of the dispersing equipment, etc., all affect the dispersion state of the fumed silica in the coating. In general, it is preferred to disperse the fumed silica into a pre-pulp before it is completely dispersed.